Prediction of the sweet/caramel aroma of beer from malt analysis

Abstract

Three important food flavour compounds, MHF [5-methyl -4-hydroxy-3(2H)-furanone], DMHF [2,5-dimethyl-4-hydroxy-3(2H)-furanone] and EMHF [5-(or 2)-ethyl-2(or 5)-methyl-4-hydroxy-3(2H)-furanone] have been identified earlier in a wide range of beers. Both DMHF and EMHF have distinctive sweet/caramel like flavours and aroma thresholds of 0.16 mg/litre and 0.02 mg/litre in water and in beer 0.3 mg/litre and 0.7 mg/litre respectively. MHF has a meaty/brothy flavour and a much higher threshold of 8.3 mg/litre. The most significant furanone in beer seems to be DMHF, which has been shown to contribute to the sweet/caramel flavour of dark lager, experimental light lagers and a range of UK ales. MHF is always found but at levels below the flavour threshold. EMHF seems to occur in measureable amounts only rarely. These compounds are known to arise during heating of sugars and amino acids and are common in a variety of thermally processed foods. DMHF is also found in fruits. Both DMHF and EMHF can be formed during yeast fermentation. However, it is not known how the whole series of steps in beer production influence the furanone content of the final beer.

The aim of this study was to identify the key steps during brewery operations which influence furanone concentration in beer and therefore may impact significantly on the flavour of the product. Laboratory beers were produced on a small scale and samples analysed for the flavour-active hydroxyfuranones throughout the process. The length and temperature of mashing, the length of boiling, the rate of cooling the worts and the effects of grist composition were investigated . Fermentation temperature and the use of stabilising agents, PVPP and Lucilite PC5 were also investigated. The results demonstrated that several aspects of beer production procedures affect the furanone content of beer but in practice because of the existing constraints on brewery procedures from other requirements, the most important factors are grist composition and fermentation temperature. Darker malts tend to produce beers with higher furanone contents but fermentation has a major affect on final concentration as yeast produces both DMHF and EMHF from, as yet, unidentified precursors. The results suggest that precursor compounds may prove to be more important than the malt furanones in determining the final furanone content of beer. A clearer understanding of the nature of the precursors should allow manipulation of their production and raises the possibility of separating beer colour and typical malt flavours.

Analysis of samples from full scale commercial ale production gave essentially the same results as the laboratory experiments but indicated that the final conditioning steps lead to reduction in furanone concentrations, particularly of EMHF.